Recently, a non-contact power transmitting device that transmits power in a non-contact manner has been widely used. The non-contact power transmitting device includes a power transmitting device that transmits power and a power receiving device that receives the transmitted power. The power transmitting device transmits power to the power receiving device in a non-contact manner through electromagnetic coupling, such as electromagnetic induction or magnetic resonance. The power receiving device includes a drive circuit that drives the power receiving device, and a load unit, such as a charging circuit of a secondary battery, which is mounted on the power receiving device.
The related art includes a non-contact power transmitting device that transmits power from a power transmitting device to a power receiving device in a non-contact manner through electromagnetic coupling between the power transmitting device and the power receiving device. A mobile terminal that is a power receiving device receives power from a charger that is a power transmitting device in a non-contact manner, and charges a secondary battery embedded in the mobile terminal.
In addition, authentication of whether the mobile terminal is correctly mounted on the charger is performed through communication using electromagnetic coupling between the charger and the mobile terminal mounted on the charger. When it is determined that the mobile terminal is correctly mounted on the charger, the mobile terminal is set as an appropriate power transmission target, and thus continuous normal power transmission is started.
Load modulation is used as a communication mechanism for authentication. The mobile terminal includes a load modulation unit. When data is transmitted from the mobile terminal to the charger, the load modulation unit changes a load thereof (internal resistance value) according to the data being transmitted, which changes an induced voltage of a primary coil in the charger.
In order to demodulate the load-modulated data signal from the mobile terminal, a reception unit in the charger performs peak hold processing for an amplitude of the induced voltage of the primary coil, and determines whether the data from the mobile terminal is logic “0” or logic “1” by comparing a peak voltage to a threshold (voltage value).
When the power is transmitted to the mobile terminal that is in close contact with a charging stand, an electromagnetic induction method is widely used. In the electromagnetic induction method, a frequency of approximately 100 kilohertz (kHz) is often used for power transmission. With the frequency of approximately 100 kHz, it is possible to provide a method of observing a change of the amplitude of the induced voltage of the primary coil as demodulating mechanism disclosed in the related art.